Re: Object#=~

--- Eric Hodel <[e-mail]> wrote:

> On 06 Jul 2005, at 09:30, Eric Mahurin wrote:
> 
> > --- Yukihiro Matsumoto <[e-mail]> wrote:
> >
> >> <[e-mail]> writes:
> >>
> >> |I expected you to say that this was intentionally
> provided
> >> |as a "third state":
> >> |
> >> |true  - positive pattern match result
> >> |nil   - negative pattern match result
> >> |false - don't know (no match was done)
> >>
> >> Hmm, sorry for behaving unexpectedly.  But I like your
> idea.
> >> Ryan, what do you think?
> >>
> >>                             matz.
> >>
> >
> > Should nil be don't know and false be mismatch?  That would
> be
> > consistent with <=> which returns nil if the items aren't
> > comparable.  Maybe the same should be done with == and ===
> -
> > return nil instead of false when the 2 objects can't be
> > compared.
> 
> $ ruby -e 'p "f" =~ /x/'
> nil

"f" vs. /x/ are comparable so I was thinking false might be
more  suitable than nil.  And use nil when it is the wrong type
of object or doesn't respond to the right methods.  I'm
suggesting that comparison operator methods look something like
this:

def ===(obj) # or <=>, ==, =~
    return(nil) if obj isn't comparable to self
    ... compare returning false instead of nil ...
end

or:

def ===(obj) # or <=>, ==, =~
    ... compare returning false instead of nil ...
rescue
    # should get here is obj didn't behave as expected
    return(nil)
end




		
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